Orbital acceleration of electron is

$\frac{n^2 h^2}{4 \pi^2 m^2 r^3}$ $\frac{n^2 h^2}{2 n^2 r^3}$ $\frac{4 n^2 h^2}{\pi^2 m^2 r^3}$ $\frac{4 n^2 h^2}{4 \pi^2 m^2 r^3}$

$\frac{n^2 h^2}{4 \pi^2 m^2 r^3}$

$m v r=\frac{n h}{2 \pi} \Rightarrow v=\frac{n h}{2 \pi m r} \Rightarrow \frac{v^2}{r}=\frac{n^2 h^2}{4 \pi^2 m^2 r^3}$